Air treating device having means for producing negative ions



April 19, 1966 c. H. WINTERMUTE AIR TREATING DEVICE HAVING MEANS FOR PRODUCING NEGATIVE IONS Filed Aug. 29, 1962 2 Sheets-Sheet 1 FIG.

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April 19, .1966 c. H.-W|NTERMUTE AIR TREATING DEVICE HAVING MEANS FOR PRODUCING NEGATIVE IONS Filed Aug. 29, 1962 2 Sheets-Sheet 2 United States Patent 3,247,374 AIR TREATING DEVICE HAVING MEANS FOR PRODUCING NEGATIVE IGNS Carlton H. Wintermute, i451 Compton Terrace, Hillside, NJ. Filed Aug. 29, 1962, Ser. No. 220,211 flaiins. (Cl. 250-43) This invention relates to improvements in air-treating devices for generating negative ions in the atmosphere through the interaction of ultraviolet radiation with a metallic screen, and more particularly, to a method and means for reactivating the metallic ion-producing screen utilized in such devices.

For some time it has been known that the presence of an abundant supply of negative ions in the air, a condition occurring naturally in certain climatic regions, has important therapeutic benefits to animal and human life. For example, persons affiicted with hay fever, asthma, and other respiratory conditions, have experienced significant relief while breathing air artificially treated with a large quantity of negative ions. Also, an atmosphere containing a large quantity of negative ions has been found to have dramatic efiects in relieving pain and promoting the treatment of hospital patients undergoing surgery or suffering from severe external wounds such as burns, skin abrasions, and the like. For persons in normal health, the breathing of air dosed heavily with negative ions is highly invigorating and refreshing. Marked improvements in mood and attitude have been observed in subjects placed in a controlled environment containing treated air.

Although all of the physiological effects of air treated with negative ions are not completely understood at this time, it is believed that the breathing of air containing an abundant quantity of negative ions increases the vibration rate of the cilia or hair-like filaments in the respiratory tract. As the cilia serve to trap and remove debris from the air breathed into the body, an increase in cilia activity lessens the concentration of smoke, soot, and other harmful impurities in air taken into the lungs. In addition, it has been theorized that the activity of certain glands in the body, such as the adrenal and the pituitary, as well as the reticuloendo-thelial system (the warrior defense cells which determine the bodys resistance to disease), are likewise stimulated by the presence of negative ions in the air.

In certain geographic regions, especially mountainous areas, there may be present naturally in the air negative ions in concentrations as high as 2,000 per cubic centimeter. Negative ion concentrations of this level have been found to be highly exhilarating and beneficial to the human body when breathed in the atmosphere. The high level of negative ions in such locations is generated and continuously replenished by the forces of nature through cosmic and ultraviolet radiation, natural radioactivity, winds, waterfalls, lightning, storms and other electrical discharges. Generally speaking, however, artificial air-treatment is required, in the greater majority of environments where there may be only a few hundred ions/cc. or so present, in order to increase the negative ion concentration to the level where the beneficial effects described above are produced.

There are at least three known methods for treating air electrically to produce large concentrations of negative ions in a controlled environment; (1) secondary emission of electrons from a radioactive source, (2) generation of electrons by electrical discharge between electrodes impressed with potentials on the order of to 50 kilovolts, and (3) removal of electrons from a material of low photoelectric work function with ultraviolet or short wavelength radiation. Of the three methods, the first two involve either exceedingly dangerous or exceedingly expensive apparatus, as well as requiring filtering means for separation out the positive ions produced. Gn the other hand, the last-mentioned method of negative ion production is the most practical from the standpoints of wide utility, economy, and safety, and accordingly, is the technique which is finding favor today.

In air-treating machines operating according to this last-mentioned method for producing negative ions in the atmosphere a source of ultraviolet radiation, typically a mercury lamp, is located in close proximity to a metal screen or plate which is maintained at high negative potential. A screen rather than a solid (unperforated) plate is generally preferred as the ion-generating element in order to permit a portion of the ultraviolet radiation to pass through unimpeded and be made available for sterilizing and, through the generation of ozone, remove odors from the circulating air stream. The screen conventionally is comprised of a so-called low energy metal, i.e., a material having a low photoelectric work function (the energy required to remove an electron from the material). Photon radiation from the ultraviolet lamp source impinges on the screen and frees electrons from the surface of the metal; the escaping electrons in turn combine with oxygen, Water vapor, and other molecules in a circulating air stream to produce negative ions.

f the metals possessing a low photoelectric work function, two of the noble metals, gold and silver which do not oxidize readily have been found to be especially suitable for the screen material in air-treating devices of this type wherein an ultraviolet radiation source is uti lized as the energizer in producing a supply of free electrons.

With a negative ion screen formed of gold or other suitable metallic material, it is possible to produce negative ions in the circulating air stream in concentrations as high as 200,000 per cubic centimeter. (Because of their short average life of approximately only seven seconds, the quantity of negative ions in the air stream diminishes rapidly, and it is therefore necessary to produce concentrations on this order at the screen for there to be a beneficial level of ion concentration available to persons in the immediate area who are breathing the treated air.) 'It has been observed, however, that the ion productivity of such a screen in an air-treating apparatus decreases at a rapid rate over a period of time independently of the amount of its utilization, and typically the concentration of negative ions produced may experience a drop to-a level of only of the initial value (e.g. 100,000 ions/cc.) after a period of only three or four Weeks. This drastic fall-off in ion production has re quired that prior art air-treating devices be substantially overdesigned in order that the negative ion concentration remain at a useful level for any reasonable period of time. Moreover, if it were desired to restore the apparatus to its initial rate of ion production, it has heretofore been necessary to remove the old screen and substitute a new one in its place. The present invention is directed to a method and apparatus for reactivating the metallic screen utilized in these air-treating devices so that the ion productivity of the screen (or more precisely,-its ability to supply free electrons to the atmosphere) stays substantially constant at its high initial value indefinitely.

I have discovered that the metallic screen can be reactivated and restored to its initial potential for ion production by the expedient of heating the screen material to a temperature substantially in the range of GOD-1,000 F. for several minutes duration. Although the cause of the sharp drop in the screens negative ion output has not heretofore been known, I believe that this condition is due to the deposit and buildup on the surface of the screen of organic and inorganic impurities during its exposure to the atmosphere. Accordingly, subjecting the screen to an elevated temperature for a short period of time apparently boils off these deposits with the result that the surface of the screen is restored to its initial ion productivity.

In a preferred embodiment of my invention, an airtr-eating apparatus of the type described, employing a metallic screen in conjunction with an ultraviolet radiation source to generate negative ions in the atmosphere, is provided with a metallic screen of novel construction which is automatically reactivated inside the apparatus, each time the apparatus is used, by the passage therethrough for a predetermined period of time of an electrical current which elevates the temperature of the screen material to the prescribed range in accordance with the process of the present invention.

It is therefore a principal objective of the present invention to provide a method and means for reactivating the negative ion screen utilized in air-treating apparatus of the type described.

It is another objective of the present invention to provide an improved air-treating apparatus of the type employing a metallic screen in conjunction with an ultraviolet source to generate negative ions in the atmosphere.

It is still anonther objective of the present invention to provide a negative ion screen for such air-treating devices which is of novel construction and is particularly suitable for reactivation according to the method of the present invention.

And it is yet another objective of the present invention to provide a negative ion screen of novel configuration for advantageously and etliciently utilizing radiation from the ultraviolet source in an air-treating apparatus of the type described.

The foregoing and other objective, features, and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.

FIG. 1 is a pictorial view of an illustrative embodiment of a negative ion screen and ultraviolet lamp source suitable for use in an air-treating apparatus according to the present invention.

FIG. 1A is an enlarged, cross-sectional view of an element of the screen mesh shown in the embodiment of 'FIG. 1.

FIG. 1B is a representative plot showing the amount of reactivation of a typical aged negative ion screen which is eifected at various heating temperatures when practicing the process of the present invention.

FIG. 2 is a schematic diagram of the electrical circuit of an illustrative embodiment of an air-treating apparatus suitably adapted for practicing the method of the present invention.

FIG. 3A is a side elevational view, and FIG. SE a front elevational view, of the exterior of an exemplary embodiment of an air-treating apparatus according to the present invention.

FIG. 4A is a side elevational view, and FIG. 43 a front elevational view, of the exemplary embodiment of FIGS. 3A-3B, with the cabinet housing removed to show the arrangement of various components in the interior of the air-treating apparatus.

Referring now to FIG. 1, there is shown a negative ion screen 30 in close proximity to a source of ultraviolet radiation 40. As depicted in this illustrative embodiment, the mesh of the negative ion screen 30 describes a cylindrical surface encircling and coaxial with a tubular lamp 40 of conventional design which emits ultraviolet radiation upon encrgization from a suitable source of electrical potential (not shown). As illustrated, the screen 30 is formed of amesh comprised of an electrically-continuous strand of a helically-wound element 31 carried and supported away from tube 40 by a pair of insulating collars 35. This screen mesh element 31 is strung in zigzag fashion between a plurality of aligned terminal lugs 36 uniformly disposed about the periphery of the respective collars 35. Although the screen mesh element 3 1 is looped in regular fashion between the collars 35 to encircle the periphery of the lamp tube 40, the ends of the mesh element are not joined together but are instead attached to a pair of separate and unconnected terminal lugs 36 to provide a single series element for the electrical circuit connections described later in regard to FIG. 2. (For purposes of clarity, a portion of the screen mesh element 3 1 has been omitted and is represented by phantom lines in the figure.)

As may be seen in the cross-sectional view of FIG. 1A, the wire-like screen mesh element 31 is comprised of a relatively thick central core 32 of a suitable resistive material, such as the nichrome alloy used in conventional electrical heating elements, and a surface covering 34 of a metal having a low photoelectric work function, such as gold, silver, or in some cases a composite coating of gold and silver. It is preferable, in accordance with the objective of the present invention, that the noble metal coating the surface of the screen mesh 31 be relatively thin, as compared with the central core 32 of resistive material, in order that the electrical conductivity of the mesh element remain relatively low and determined substantially by the properties of the core material. In one good embodiment of the invention, the mesh element 31 of the screen 30 has a central core of nichrome metal alloy of approximately 10 mils thickness, and a surface layer 34 of silver on the order of 2-3 mils.

Referring again to the illustrative embodiment of FIG. 1, it may be seen that the cylindrical mesh of the screen 30 is coaxial with the axis of the ultraviolet lamp tube 4!) and extends therealong for a major portion of its length. Therefore, an appreciable number of the photons of ultraviolet radiation emitted from tube 40 will impinge upon the surface coating 34 of the screen mesh element 31; and, with the screen maintained at a suitable negative voltage by a source of DC. potential (not shown) applied across the terminal ends of the mesh element 31, electrons will be liberated from the metal for combination with oxygen and other molecules in the atmosphere to form negative ion particles.

As it is usually desirable that ultraviolet radiation from the lamp source 40 he used for sterilization and deodorization purposes, as well as for the production of negative ions in the atmosphere, it is necessary to divide the use of the available ultraviolet radiation between the respective purposes. I have discovered that radiation emitted from an ultraviolet lamp source is utilized in a particularly eiiicient manner when approximately 10% of the effective radiation-producing surface of the lamp is shaded by the mesh of the negative ion screen 3!). In other words, a particularly advantageous arrangement of the negative ion screen 30 and the ultraviolet lamp as is obtained in an air-treating apparatus when the configuration of the screen mesh is such that approximately of the ultraviolet light generated passes through the screen unimpeded and is made available for air sterilization and the production of ozone.

It is to be understood, or" course, that the principles of the present invention are likewise applicable to lamp and screen configurations other than the types shown in the illustrative embodiment of FIG. 1. For example, a conventional spherically-shaped ultraviolet lamp may be readily provided with a suitably adapted screen array comprised of a mesh element similar in construction to that shown in the figures. in some variations it may be desirable to provide a negative ion screen having a mesh of cross-hatched or rectangular grid configuration, similar to conventional'window screening insofar as pattern of design is concerned, rather than the helical spring a) type of mesh element shown. Again, for efficient utilization of the ultraviolet radiation source, it would be desirable in such variations to have the configuration and fineness of the screen mesh be such that approximately 90% of the radiation passes through the screen without interception.

As previously stated, a negative ion screen formed of a surface coating of a low energy metal exhibits an aging in its ion productivity in a relatively short time. This aging occurs independently of the amount of use of the screen in conjunction with an ultraviolet radiation source in an air-treating apparatus. In the practice of the present invention, reactivation of such a screen, that is, restoration to its initial high level of ion production, is accomplished by heating the screen to an elevated temper-ature within a prescribed range for a short period of of time.

FIG. 1B is a representative curve illustrating the reactivation in ion output which is effected when a typical negative ion screen, of the construction described, is heated to an elevated temperature. The ordinate of the curve is the negative ion output of the screen, in thousands of ions/00., when exposed to ultraviolet radiation; the abscissa is the reactivation temperature required, in degrees Fahrenheit, to achieve a particular maximum ion output. [Since aging of the screen material cornmences immediately after reactivation of the screen by heating ceases, the maximum or initial value of ion output exists only so long as the screen is undergoing reactivation, and therefore points on the curve shown in FIG. 13 represent the negative ion output of the screen material immediately after it has been reactivated by heating to the particular temperature indicated and before subsantial aging recurs] As may be seen from the curve, which is based on experimental data obtained with a group of similar negative ion screens of gold-and-silver material whose respective ion outputs had dropped due to aging to a level of 50,000 ions/co, heating of the metallic screen material to elevated temperatures causes a steady rise in its negative ion output, as the temperature is increased, until a peak value is reached in the range between BOO-900 F. At this peak value the reactivation of the screen is such that its negative ion output productiviy is substantially restored to the level which it possessed initially, at the'time of its manufacture, before aging occurred. Further temperature elevation, above the point at which maximum screen reactivation occurs, results in a decrease in the maximum ion output obtained when the screen is later cooled down to ambient temperature level for use in air-treating apparatus. At very high temperatures (above about 1200 P.) very little, if any, reactivation of the screen material occurs.

Although the following temperature limits are not critical, I have found that the best results in reactivation are achieved when the metallic screen material, whether it be gold, silver, or a composite of the two, is heated to a temperature substantially in the range 600-1,000 F. Outside this range the amount of reactivation which can be effected falls off sharply. In order to accomplish reactivation of a negative ion screen according to the process of the present invention, I have found that it is only necessary to heat the screen material and maintain it at a temperature within this prescribed range for a few minutes (e.g., 35 minutes) duration; heating for longer periods of time (e.g., several hours) does not appreciably affect the amount of reactivation which occurs.

FIG. 2 is an electrical circuit schematic of an exemplary apparatus for practicing the method of the present invention. In particular, this figure illustrates an airtreating apparatus of the type described wherein reactivation of the metallic screen, used in conjunction with a source of ultraviolet radiation for producing negative ions in the atmosphere, is accomplished automatically 6 each time the apparatus is used by the consumer. The reactivation is effected by connecting the screen, which is of the type shown in FIG. 1 comprising a mesh element formed of a central core of electrically resistive material overlaid with a thin surface coating of a metal of low photoelectric work function, directly across the line power supply for a predetermined period of time after the air-treating device has been turned to the off position.

In this position, a normally-open thermal switch, which has become energized during operation of the device while in the on position by heat produced from the ultraviolet lamp source (or from a separate heater in series therewith), provides a circuit connection between a source of electrical potential, e.g., the power line, and the screen. This connection is maintained for several minutes duration after the machine has been turned to the off position until the deenergized lamp has cooled down sufiiciently for the contacts of the thermal switch to open, thereby breaking the circuit. During the time when the thermal switch is closed, the application of line potential across the screen causes the screen mesh, due to the construction of it central core of resistive material, to be heated in short order to a temperature of approximately 1,000 F. and maintained there until the thermal switch eventually opens, thus reactivating the metal-lie surface coating of the screen in accordance with the method of the present invention. Turning more specifically to the embodiment depicted in FIG. 2, there is shown therein a source of AC. potential which typically may be the conventional volts household power line. A double-pole-double-throw (D.P.D.T.) switch 119 is connected at the input when the air-treating device is plugged into the power line, and the position of its ganged pair of switch arms determines the on-and-off modes of operation for the apparatus. For the position shown in the drawing, the machine is on the on mode with the arms of the D.P.D.T. switch 1110 making contact with respective terminals 11% and 1100'. In this mode a portion of the AC. power supplied by the alternating potential source 100 is rectified to provide a D.C. potential of approximately volts for application to the negative ion screen 30. The screen 3}) is maintained at this negative voltage during operatron in the on mode in order to prevent the build-up of a positive charge as electrons are liberated from the screen. Illustrative means for providing this D.C. screen voltage may suitably comprise an isolation transformer 120 and a half-wave rectifier circuit, including currentlimiting resistor 122, diode 124, capacitor 126, and bleeder resistor 128. As there is no connection between the negative ion screen 30 and ground, there is but negligible current drain on the D.C. power supply, and the screen accordingly assumes a negative potential approximating that of the peak of the AG. waveform appearing across the secondary of the transformer 120.

In the on mode a source of photons for interaction with the ion-producing screen is provided by UV lamp 40 which is connected through heater resistor 152 and balast coil 142 across the A.C. potential source 100. Ballast coil 142 acts as an autotransformer to supply the stepped-up voltage required for operation of the ultraviolet larnp 40. Also connected to the power line when the air-treating device is in the on mode of operation is motor 160, which drives a blower fan for impelling air through the apparatus, and a series resistor 164. If desired, the resistor 164 may be shunted with a shorting switch 162, as shown, to provide two-position speed control of the blower.

When the air-treating device has been operated in the on position for a short period of time, normally-open thermal switch 158, which may be of the bimetallic element or other suitable type, is activated by infrared radiation emitted from heater resistor 152. (If desired, the separate heater element may be eliminated and, by placing the thermal sensing element in close proximity, the normally-open thermal switch made responsive to heat radiation from the lamp to itself.) However, with the apparatus still in the on mode of operation, no additional circuit connection results from the closing of the contacts of the thermal switch 159. No change in the operation of the apparatus occurs until after the D.P.D.T. switch H is thrown to the second position (the off mode) when the user is through for the time being with operation of the air-treating device.

in th off mode the arms of the D.P.D.T. switch 110 are connected respectively to terminals 110a and 110s, and the rectifier circuit providing the DC. potential for the screen, as well as untraviolet lamp in and blower motor 160, are all then disconnected from the AC. power supply 100. At the same time, the terminals of the negative ion screen 36 are placed directly across the alternating supply 100, the circuit being completed through thermal switch 150, which has been previously closed by heat radiated from heater 152 in series with ultraviolet lamp 40 during the on mode of operation of the apparatus. Although the heater and the UV lamp are now de-energized, thermal switch 150 will remain closed for several minutes duration until suificient cooling has occurred for its switch contacts to open. It is primarily during this period of time, when the normallyopen thermal switch is closed and the negative ion screen 30 is connected directly across the potential source 100, that reactivation of the screen takes place according to the method of the present invention.

As stated previously, maintenance of the screen at a temperature substantially in the range of 600l,000 F. for several minutes permits the ion productivity of the layer of metal material covering the surface of the screen to be renewed. Accordingly, the total electrical resistance of the elements comprising the mesh or" the screen 3% is suitably designed in such manner that the application of a predetermined potential (such as the nominal value of the full line A.C. potential, e.g. 120 volts) across these screen elements results in a temperature rise to a level within the prescribed range. It is to be observed that, as the material coating the surface of the screen and overlying its central core of resistive material is of low photoelectric work function and thus of relatively high electrical conductivity, the overall resistance of the screen will be somewhat less than that of a screen made entirely of resistive material.

After a period of several minutes, thermal switch 150 cools down sufficiently for its contacts to open (it is located relatively remotely from the screen 30 so as not to be heated thereby), thus disconnecting screen 39 from the potential source 100, whereupon the reactivation process ceases as the temperature of the now de-energized screen proceeds to fall below the lower limit of the prescribed range towards that of the ambient environment. With thermal switch open, and the screen reactivation process now completed, the air-treating device will remain in a completely dormant state in the off mode, with all elements electrically de-energized, until the apparatus is again switched into the on mode of operation.

FIGS. 3A-4B show an exemplary embodiment of an air-treating apparatus constructed according to the teachings of the present invention. In FIGS. 3A3B the exterior of the air-treater is shown, and in FIGS. 4A-4B the cabinet housing has been removed to show the interior arrangement of the various principal components. (For the sake of clarity, electrical leads and wire connections between components have been omitted from these figures).

As shown in this illustrative embodiment, the airtreater is housed in a compact cabinet 2th) with an airintake port 210, 222 located in each of the two sides of the cabinet housing. Removable filters 212, 222, which may be of conventional design and comprised of charcoal and/or fiberglass material, are fitted across the air-intake ports 210, 220 for the purpose of trapping and screening out large dirt particles present in the atmosphere. Air, after its conditioning by the air-treating apparatus, is impelled out from the front of the cabinet housing through air exhaust ports 230. The air flow is such that untreated air drawn in by the apparatus through intake port 210 is exhausted through the left-hand one of the ports 230 shown in FIG. 3B, and correspondingly, lair taken in through port 220 is exhausted through the right-hand port 23%).

Referring now to FIGS. 4A4-B, there are shown views of the air-treating apparatus with the cabinet 2% removed and its components supported on a chassis 240. A pair of blowers 16th: and 16% are associated, respectively, with the left-hand and right-hand air intake and exhaust ports. These blowers are driven by a common motor 160 whose speed may be changed, if desired, by toggle switch 162, as in the manner shown in the electrical schematic of FIG. 2.

Air drawn in through the respective intake ports 210, 22.0 through the filters 212, 222 is directed by the blowers 160a, lfitlb past the negative ion screen 36, which is in close proximity to a lamp 4% providing ultraviolet or other suitable short-wavelength radiation. The negative ion screen 30 may be of the construction hereinbefore shown and described in connection with FIG. 1, and the juxtaposed radiation source 40 may be an ultraviolet lamp of known design such as Westinghouse Sterilamp Model 18211-10. In flowing past the negative ion Screen 36, the air is liberally dosed with negative ions and, in addition, is sterilized and some of its oxygen molecules converted to ozone by that portion of the UV radiation from the lamp it which is not directly incident upon the screen elements. This treated air is then forced, at high velocity, out of the exhaust ports 230 in the front of the apparatus and into the surrounding environment.

The other principal components on the air-treating apparatus, described in connection with the diagram of FIG. 2, are shown, in FIGS. 4A-4B, illustratively mounted in a suitable arrangement on the chassis 24-h. Thermal switch 15% is shown disposed on the neck of the ultraviolet lamp 40 and energized directly by heat radiation therefrom, rather than by a separate heating resistor. Terminal board 245 supports several of the smaller electrical components such as resistors, capacitors, diodes, etc. Also shown in a packaged assembly mounted on the chassis 240 of the air-treating apparatus are the lamp ballast 142, the isolation transformer 128 for the rectifier circuit, and the D.P.D.T. toggle switch for controlling the mode of operation of the device.

The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. Air-treating apparatus for producing negative ions in the atmosphere comprising, in combination, a source of ultraviolet radiation, an electron emitter having a surface coated with a metallic material of low photoelectric work function taken from the group consisting of gold, silver, and the combination thereof, said emitter being normally maintained at ambient temperature and generating free electrons into the atmosphere by photoelectric emission when subjected to ultraviolet radiation from said source, means for circulating air past said emitter, and means for periodically heating said surface of said emitter to an elevated temperature substantially in the range 6001,000 F. for about 35 minutes duration in order to cause reactivation of the photoelectric emission properties of said emitter.

2. Air-treating apparatus for producing negative ions in the atmosphere comprising, in combination, an ultraviolet lamp energized from a source or" electrical power, an array of electrically resistive elements having a surface coating of metallic material of low photoelectric work function, means for obtaining a negative DC. potential from said source, means for circulating air past said array, said apparatus in a first state of operation having said array maintained at said negative DC potential while subjected to ultraviolet radiation from said lamp, and means for switching said apparatus into a second state of operation wherein sufiicient electrical current from said source is passed through said electrically resistive elements of said array to cause the surface coating thereof to be heated to an elevated temperature.

3. Apparatus as set forth in claim 2 wherein said metallic material is taken from the group consisting of gold, gold-and-silver, and silver.

4. Apparatus as set forth in claim 2 including timing means for limiting the duration of said second state to a predetermined length of time.

5. Air-treating apparatus for producing negative ions in the atmosphere comprising, in combination, a source of AC. electrical power, an ultraviolet lamp energized from said source, a heating element in series with said lamp, a screen comprised of electrically resistive elements having a surface coating of metallic material of low photoelectric work function, rectifying means for obtaining a negative DC. potential from said A.C. source, means for circulating air past said screen, said apparatus in a first state of operation having said screen connected to said rectifying means and maintained at said negative D.C. potential while being subjected to ultraviolet radiation from said lamp, and thermally-actuated switching means juxtaposed near said heating element and responsive to heat generated therefrom for maintaining said apparatus in a second state of operation for a predetermined period of time when said lamp and heating element are de-energized by disconnection from said source, whereby sufficient current from said source is passed through said electrically resistive elements of said screen in said second state of operation to heat said surface coating to an elevated temperature for said predetermined period.

References Cited by the Examiner UNITED STATES PATENTS 2,715,195 8/1955 Friedman 313-101 X 2,732,501 1/1956 Blacker 250-43 2,151,785 3/1959 Lubszynski et al 313101 2,932,759 4/1960 Shepherd 313346 X 3,072,978 1/1963 Minto 250-43 X 3,128,378 4/1964 Allen et al. 250-43 OTHER REFERENCES The Emission of Electricity From Hot Bodies, pages 200 to 210, by O. W. Richardson, 1921, QC701R5.

RALPH G. NILSON, Primary Examiner.

30 FREDERICK M. STRADER, Examiner. 

1. AIR-TREATING APPARATUS FOR PRODUCING NEGATIVE IONS IN THE ATMOSPHERE COMPRISING, IN COMBINATION, A SOURCE OF ULTRAVIOLET RADIATION, AN ELECTRON EMITTER HAVING A SURFACE COATED WITH A METALLIC MATERIAL OF LOW PHOTOELECTRIC WORK FUNCTION TAKEN FROM THE GROUP CONSISTING OF GOLD, SILVER, AND THE COMBINATION THEREOF, SAID EMITTER BEING NORMALLY MAINTAINED AT AMBIENT TEMPERATURE AND GENERATING FREE ELECTRONS INTO THE ATMOSPHERE BY PHOTOELECTRIC EMISSION WHEN SUBJECTED TO ULTRAVIOLET RADIATION FROM SAID SOURCE, MEANS FOR CIRCULATING AIR PAST SAID EMITTER, AND MEANS FOR PERIODICALLY HEATING SAID SURFACE OF SAID EMITTER TO AN ELEVATED TEMPERATURE SUBSTANTIALLY IN THE RANGE 600-1,000*F. FOR ABOUT 3-5 MINUTES'' DURATION IN ORDER TO CAUSE REACTIVATION OF THE PHOTOLECTRIC EMISSION PROPERTIES OF SAID EMITTER. 